Which of these numbers is composite? ${7,\ 37,\ 43,\ 68,\ 73}$
Solution: A composite number is a number that has more than two factors (including 1 and itself). 7, 37, 43, and 73 each have only two factors. The factors of 68 are 1, 2, 4, 17, 34, and 68. Thus, 68 is the composite number.